Certain special chairs have been manufactured, in which it is possible to raise the seat and then lower it again, in order to allow the occupant to regain a standing position without straining the leg muscles. One such chair is described in U.S. Pat. No. 3,915,494, issued Oct. 28, 1975 to David Somerset. The Somerset chair is one in which the seat frame is guided along a path inclined forwardly from the vertical, so that raising and lowering movement of the seat frame is accompanied by forward and backward movement respectively. The raising of the seat frame is accomplished by means of cables passing over a complicated array of pulleys, and reeled in on a capstan which is rotated at a slow speed through a speed-reducing mechanism by an electrical motor mounted in the base of the chair.
Besides being quite expensive, the Somerset structure has a large number of critical moving parts, pulleys, slideways and the like, of which the malfunctioning of even one can result in jamming or inoperability of the chair.
It is an aim of one aspect of this invention to provide a chair structure in which the seat portion is capable of being raised and lowered, but which is such that it can be manufactured very inexpensively from standard and easily obtained parts, and which in particular avoids mechanical complexity by using a pneumatically powered air bag to accomplish the raising of the seat.